There has been developed an optical card in which an optical recording medium film is sputtered or evaporation deposited onto a card-shaped substrate and various data is recorded as a track train onto the optical recording medium film.
Namely, a laser beam modulated by a digital signal is scanned through a galvano mirror and irradiated onto the optical card, so that recording tracks are formed onto the optical recording medium film and data is written. The reflection factor of the portion in which the track was formed is changed in accordance with the recording data.
The data recorded on the optical card is read out by irradiating the light onto the track formed on the optical recording medium film of the optical card and by receiving the reflected light. Since the reflection factor of the portion in which the track was formed is changed in accordance with the recording data, the data can be reproduced from the reflected light. The data may be also read out in a manner such that a laser beam is scanned and irradiated along the track through a galvano mirror and the reflected light is detected by a photo detector or that the light from a light emitting element is irradiated onto the track and the reflected light is received line by line using a line sensor consisting of an image pickup device such as a charge coupled device (CCD) or the like.
This optical card is a recording medium of the WORM (write once, read mostly) type and data can be once written. However, the data cannot be erased and the rerecording cannot be performed.
It is a feature of the optical card that the memory capacity is remarkably larger than that of the magnetic card. Therefore, for example, the data indicative of the balance of the bank deposit, the data concerned with the medical patient's chart, or the like can be recorded on the optical card. In this manner, various kinds of services can be realized using the optical card.
Error correction codes are added to the recording data on the optical card to prevent the deterioration of the optical card and to improve the reliability. The error correction codes are applied in a sector unit basis so that the powerful error correction can be performed, wherein the sector is constituted by a plurality of tracks as one unit.
FIG. 1 shows such an optical card and an outline of an apparatus for reading out the optical data recorded on the optical card by use of a line sensor. Reference numeral 101 denotes an optical card and 102 denotes a stripe-shaped optical recording medium film of the optical card 101 (the shape of this film is not necessarily the stripe shape). Optical dot data is recorded in the recording stripe 102 along a plurality of recording tracks T. Numerals 104 and 104 indicate guide rollers to move the optical card 101 in the direction of an arrow a. A lens (cylindrical lens) 106 is arranged over the optical stripe so as to form the image of the dot data of the recording tracks T onto a line sensor 105.
Therefore, by feeding the optical card 101 in the direction of the arrow a by the guide rollers 104 and 104, the dot data of the recording tracks T, T, . . . which were image formed on the line sensor 105 consisting of a CCD or the like can be sequentially read out.
In this case, the width of the recording track T is, e.g., about 16 .mu.m. In general, the optical card 101 is fed at a pitch of, e.g., 2 .mu.m by a stepping motor (not shown), thereby sequentially reading out the dot data which was image formed on the line sensor 105 by a scan signal.
Therefore, as shown in FIG. 2A, when the arrangement direction Z of the line sensor coincides with the direction X of the recording track T, the optical data can be accurately read out from the pixel signal which was read out by the scan signal when timing marks T.sub.s written in the upper and lower portions of the recording track were detected.
However, when the accuracy of the feeding mechanism of the optical card 101 is bad, as shown in FIG. 2B, the arrangement direction Z of the line sensor obliquely crosses the direction X of the recording track T, so that the optical data of the recording track T cannot be accurately read out.
As described above, hitherto, the data written on the optical card is read by a method whereby a laser beam is irradiated along the track through a galvano mirror and the reflected light is detected by a photo detector or a method whereby the light from a light emitting device is irradiated onto the track and the reflected light is received by a line sensor consisting of an image pickup device such as a CCD or the like.
In the case of reading out by scanning and irradiating a laser beam, if the laser beam is not scanned along the track, the complete recording data of one track cannot be obtained. On the other hand, in the case of using a line sensor, if the image forming angle of the line sensor does not coincide with the angle of track, the complete recording data of one track cannot be derived. The accuracy of the feeding mechanism of the optical card needs to be raised so as to make the scan direction of the laser beam coincide with the direction of the track or to make the image forming direction of the line sensor coincide with the direction of the track. However, in order to improve the accuracy of the feeding mechanism of the optical card, it is necessary to improve the dimensional accuracy of the optical card and the accuracy of the feeding mechanism of the reading apparatus. Therefore, the improvement of the accuracy of the feeding mechanism of the optical card results in an increase in cost. In addition, there is a limit of the improvement of the accuracy.
Therefore, in the case of reading out the optical card by scanning the laser beam, hitherto, the laser beam is controlled so as to scan the recording track by way of the tracking servo. On the other hand, in the case of reading out by the line sensor, for example, as shown in the Official Gazette of Japanese Patent Laid-open Publication No. 138378/86 (W086/03611), there has been proposed a method whereby a timing signal formed on the recording track is detected, the difference between the image forming angle of the line sensor and the angle of the recording track is obtained, and the cylindrical lens to form the optical data image onto the line sensor is rotated so as to eliminate the difference.
However, as described above, in order to perform the tracking servo control and to control the image forming position of the line sensor, a circuit to perform the feedback control and an actuator for this purpose are necessary. Thus, the structure becomes complicated and the cost increases.
It is, therefore, an object of the present invention to provide an optical card reproducing apparatus which can completely reproduce the recording data even when the scan direction of the beam or the direction of the line sensor is inclined with respect to the recording track.
Another object of the invention is to provide an optical card reproducing apparatus in which there is no need to perform a complicated feedback control, the constitution is simple, and the cost can be reduced.